Electronic tension control apparatus



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TORQUE VS SPEED CURVES FOR VARIOUS THICHNESSES OF MATERIALS. SLOPESINCREASE WITH INCREASE OF MATERIAL THICKNESS.

O MOTOR AMPS.

Jwwm 2O mOPUdQ UDOGOP Ratented May 10, 1949 ELECTRONIC TENSION CONTROLAPPARATUS Anthony Winther, Kenosha, Wis., assignor to Martin P. Winther,Waukegan, 11]., trustee Application May 4, 1944, Serial No.- 534,111

18 Claims. 1

This invention relates to electronic control apparatus, and with regardto certain more specific features, to tension control apparatus for moreclosely controlling the speed of and tension in material which isunwound or wound.

Among the several objects of the invention may be noted the provision ofreliable means for providing substantially uniform linear speed andtension inmaterial which is being unwound for processing and rewound,with gradually decreasing and increasing roll diameters in the unwindingand winding processes respectively; the provision of means of the classdescribed which will automatically smoothly adjust torque to rolldiameter so as to reduce it according to lower roll diameters andincrease it according to greater roll diameters; the provision ofapparatus of the class described which at the beginning of a windingoperation will allow for overriding operator control; and the provisionof apparatus of this class which in a given design is, withoutredesigning, applicable to a wide variety of materials requiring widelydifierent tensions. Other objects will be in part obvious and in partpointed out hereinafter.

The invention accordingly comprises the elements and combinations ofelements, features of construction, and arrangements of parts whichwillbe exemplified in the structures hereinafter described, and the scope ofthe application of which will be indicated in the following claims.

In the accompanying drawings, in which is illustrated one of variouspossible embodiments of the invention,

Fig. 1 is a diagrammatic mechanical and electrical layout showing ingross the relationship between various units employed;

Fig. 2 is a complete wiring diagram of one of the control units shown inFig. 1;

Fig. 3 is a wiring diagram of a principal rectifier circuit I;

Fig. 4 is a wiring diagram of a basic voltage supply circuit II and aconnected tilting bridge circuit III;

Fig. 5 is a wiring diagram of four control circuits IV, V, VI and VII;

Fig. 6 is an illustrative diagram but not to scale ofthe wave actions ofcertain rectifier tubes;

Fig. 7 is a diagram similar to that of Fig. 6, showing the results ofcertain resistance adjustments; and,

Fig. 8 is a plot showin relationships between speed, torque andelectrical conditions under certain operating conditions.

Similar reference characters indicate corresponding parts throughout theseveral views of the drawings.

Often it is necessary to process wound material by unwinding it from onereel, passing it through a processing machine, and then winding it uponanother reel. For the present purpose, the material may be considered tobe raw material on the reel from which it is unwound and finishedmaterial on the reel into which it is wound. In between it passesthrough the processing machine, which may, for example, be a rollingmill, calendering machine or the like.

Two main problems are involved. One is to retard the reel deliverin theraw material so as to maintain a proper and substantially uniformtension in the raw material, and the other is to wind up the finishedmaterial under conditions which maintain a proper and substantiallyuniform tension therein. Thus it becomes desirable that the torque(moment) applied to a reel shall be lower when the roll diameter issmaller and higher when the roll diameter is larger. Inasmuch as theaccumulating material in eifect applies an increasing torque arm to thetensioned material, it is apparent that, for a substantially constanttension or force at the longer arm,

the applied torque should be increased as the material is wound onto awind-up reel. Also, as material is unwound from a pay-oil reel theretarding torque must be decreased as the material is unwound. All thismust be accomplished preferably at some constant linear velocity whichis an optimum for the finishing machine. The tension desired is of adifferent optimum for each material being handled.

Eddy-current clutches are peculiarly well adapted to the above mentionedconstant-tension type of service, except that when once designed for agiven application, they are not always effective for another, except byuse of the present invention. A former one of these eddy-currentclutches, with a governor for velocity control, is shown, for example,by United States Patent 1,982,461, dated November 27, 1934. Thus becauseof the wide range of tensions required for different materials, as wellas the wide speed 'ranges over which units of this class must operate,it is desirable to have a definite control of the torque, as well as ofthe speed of certain eddycurrent clutches, for reeling and unreellng.

Referring now more particularly to Fig. 1, there is shown a materialprocessing machine P driven from a three-phase A. C. motor PM through asuitable mechanical drive which includes a drive shaft DS. The motor isenergized from the wires 3 L-I, L2 and L-S of a 60 cycle three-phase A.C. circuit. A main switch SW-6 completely contros energization of thisA. C. circuit.

At UW--I is a pay-off or unwind reel which carries on its core UW-Cwindings WO of raw matrrial RM. This material RM passes to theprocessing machine P and emerges as finished material FM, the latterpassing to the windings WU on a core WP-C of a wind-up orfinishedmaterial reel WP-l. Both of the reels UW--I and WP-I rotateclockwise. The machine P drives UW-I, RM acting as a flexible connector.WP-I is driven to maintain tension in FM.

Reel WPI is driven by means of a shaft OP-Z from the field member F--2of an eddycurrent slip clutch EC2. The inductor drum EA--2 of the slipclutch is driven by means of an A. C. motor WM, the latter being fed bysaid A. C. circuit.

At CB-I is shown in general an electronic control composed of theelectronic circuit hereinafter described. This is for controlling theelectromagnetic field of the field member F2 of the slip clutch EC2 soas to tighten or loosen the magnetic coupling and thus controlling theslip, and hence the velocity and the torque transmitted, as will appear.The electronic circuit of the control CB-i is energized from said A. C.circuit. It is connected to the windings of field member F2 by circuitCB-Z and slip rings 03-3. The slip between the armature drum EA-2 andthe field member F-2 of the clutch 130-2 increases as the field strengthdecreases and vice versa. The armature EA-Z overruns the field F-Z inthe direction of rotation of the shaft OP-2 for wind-up operation. Thisdirection will be designated herein as forward. Shaft OP2 drives an A.C. generator GN-l connected to CB-I The reel UWI is rotated forward bywithdrawal therefrom of the raw material RM. In order to maintain propertension on this withdrawn material, a braking action is supplied bymeans of a second eddy-current slip clutch CCW having an armature EAIdriven backward from a motor PW. The clutch CCW includes a field memberF-l connected to the reel UW--l by means of a shaft OP-I. Since thefield member FI rotates in the same direction as the field member F-2and the armature EAI is driven backward by the motor PW, an inductivebraking action is exerted by EAI on F-i as long as the field member F-Iis energized.

Thus torque from motor PW is used as a brake on UW-l to maintain tensionin raw material RM.

As indicated, the motor PW is also energized from the A. C. circuit. Anelectronic control unit CB-J is fed by said A. C. circuit and in turncontrols the field circuit of field F--I (see line C'.B5 and slip ringCB6). Generator GIN-4 is driven from shaft OP--I and is electricallyconnected to CB-l.

Phase L-l of the A. C. circuit energizes current transformers T--IIIwhich respectively feed the control units 03-4 and CB-I. An A. C.generator GN--I driven by machine P is connected to feed both units 03-4and CBI.

In Fig. 2 is shown the wiring diagram of the contents of the controlunit CBI. Since the contents of the control box CB-4 operate accordingto the same principles as those of the box CB-I, detailed description ofthe latter will be sufiicient to gain a complete understanding of theinvention. This circuit has seven main divisions as follows, referringto Fig. 2 in general:

(1) A principal D. C. \rectifier circuit I (Fig. 3);

(2) A main or basic voltage supply circuit II with the usual filters andregulators for maintaining constant voltage (Fig. 4);

(3) A tilting bridge circuit III (Fig. 4);

(4) A manually-controlled adjustable reference voltage circuit IV (Fig.5);

(5) An auxiliary machine-speed-controlled reference voltage circuit V(Fig. 5);

(6) A clutch speed control circuit VI (Fig. 5); and,

(7) A clutch torque control circuit VII (Fig. 5).

Circuits IV and V are connected in voltage aiding sequence and so arecircuits VI and VII, but the voltage sum from IV and V, and voltage sumfrom VI and VII, are arranged for voltage opposition. Also, circuits Vand/or VII may at will be out out without changing the oppositionrelation of the residual voltages. How this may be done will appear.

Referring to the principal rectifier circuit I, similar ones have beendescribed in my Reissue Patent 22,432, dated February 1, 1944, and inPatent 2,277,284, dated March 24, 1942. This circuit I consists of atransformer Tl having a primary winding connected across the lines Ir2and L3 of the A. C. circuit. The secondary S of this transformer T--I isconnected at its opposite ends to the anodes of a pair of threeelement,hot cathode, gas-filled, grid-controlled rectifier tubes I and 2 of thehalf-wave type. These tubes require proper grid potential to fire. Theyare characterized by the fact that the grid of each tube can start theanode current, but cannot shut it off. However, when the alternatinganode voltage passes through zero, the current dies out automatically.The effect of the grid action is to start the respective tube firing atone point or another on one swing of the A. C. anode voltage wave.Different total average D. C. currents are passed as determined by thegrid actions. A two-anode amplifier tube 3 in the tilting bridge circuitIII effects alternate firing of tubes I and 2, its anodes beingrespectively connected with the grids of tubes I and 2.

A mid-tap I2 of the secondary S is connected to one end of the fieldcoil CL of the slip clutch EC-2. The coil CL is in the slip clutch ETC-2which has been diagrammed at the lower part of the figure. To avoiddiagram complexities the coil CL has been shown twice. In the upper partof the diagram it is located in the circuit and in the lower part itsmechanical location only is indicated with respect to the field memberF-2, without showing it in the circuit.

The other end of the field coil CL is connected to the mid-tap I3 of atransformer T2, the primary of which is connected across lines L-l andL2. The opposite ends of the secondary of the transformer T2 areconnected in parallel with the cathodes of the respective tubes I and 2.Control of the tubes I and 2 is managed by means of grids GI and (3-2respectively. Resistances R--I limit the current flowing through thegrids so that they are substantially voltage controlled from the anodesof tube 3. When the tubes I and 2 fire (which occurs alternately, aswill appear), the anodes alternately feed direct current to oppositeends of the secondary S. Thus direct current flows from the center tapI! of transformer Tl through the coil CL and to the center tap I3 of thetransformer T2.

Alternating current applied to circuit I from the secondary oftransformer T--2, proceeds to the cathodes of the tubes I and 2 and isrectified to produce said direct current. The transformer T2 isconnected 120 out of phase with respect to the transformer TI, beingconnected across L-I L-2. The effect of this in connection with otherparts of the circuit will appear.

In view of the above, it will be seen that the secondary S oftransformer TI applies an alternating voltage to the anodes of the tubesI and 2. Whenever the grid G-I and anode of the tube I are positiveenough, its cathode.

passes current toward the anode and through the clutch coil CL. Thusthis tube becomes a halfwave rectifier. The action of the'tube 2 issimilar, but alternating with respect to the action of tube I. The solidarrows in Fig. 3 illustrate an exemplary fiow of electrons when theyoccur through tube I.

As stated, circuit II is a main reference voltage circuit. By its meansreference voltage is established for setting a main level of potentialfor controlling the grids of the principal rectifier tubes I and 2. Thisreference voltage circuit II originates in a secondary component of atransformer T -5, the latter being fed from the lines L-I and L-Z.Rectified negative current under a given voltage issues from the cathodeof tube 5, induced by the action of the transformer T-- (see the solidarrows, Fig. 4). The cathode is heated by connection XX from a secondarycomponent of a cathode supply transformer T-3, the iatter being fed fromthe lines L2 and L-3. Thus voltage is applied from the mid-tap of T-5through points 29, 30 and then to point I 1. Here the circuit splits,part of the voltage being applied through resistance R5, and part beingapplied to the 'cathode of the amplifier tube 3. The heating element ofthe cathode of tube 3 is connected to a secondary component ZZ of saidtransformer T-3. Thus voltage is impressed upon the anodes of tube 3 andthe circuit is completed to tube 5 via resistances R--2, R-3, points I5and 3|, resistance R-6 and choke KI back to the cathode of tube 5. Thecircuit is completed as indicated by the solid arrows in Fig. 4 whenevertube 3 fires an anode.

Condenser C-I cold cathode tube 4, resistance Rr-G and choke KI arerelated so as to effect filtering and regulation to maintain constantvoltage conditions in circuits II and III. Tube 4 acts as a voltageregulating leak. Details of this type of voltage regulation have alsobeen specified in my U. S. patent applications, Serial No. 513,057,filed December 6, 1943, now abandoned, and Serial N0. 519,783, filedJanuary 26, 1944, now Patent No. 2,411,122, issued November 12, 1946.

Resistance R-5 is connected with resistance R- at point I4. ResistanceR-4 connects with point I5. The midtap I 3 of the transformer T-2 isconnected with the point I4 between the resistances R5 and R4.Resistances Rr '5, R-4, the tube 3, and the resistances R--2 and R-3,considered alternatively, constitute a bridge through which voltage ongrids GI and G2 is applied.

The rectifier tube 3 has grids G-3 and G-4 controlling fiow of negativeelectrons to its respective anodes and the respective anodes feed thegrids G-I and G2 of the rectifier tubes I and 2 respectively,resistances R-I being used in the circuits of said grids G-I and G-2.Thus when either of the grids G-3 or G-4 is relatively negative withrespect to the cathode of tube 3, the firing of the latter is suppressedto the respective anode. When either of these grids is relativelypositive, the tube 3 fires to the respective anode. When tube 3 fires,this increases the negative electrons in grid G-I or G-2 of tubes I or2, tending to suppress firing of the relevant one of these tubes. Whengrid GI or G--2 is starved of negative electrons, that is, when therelevant part of tube 3 does not fire, then the respective grid G-I orG2 becomes relatively positive and the relevant tube I or 2 fires. tofire when the relevant anodes of tube 3 do not, and vice versa.

The grids G-3 and G4 of tube 3 are supplied through resistances Rr-lfrom the secondary of a transformer T4. The primary of a transformer T-4is energized from the cathode circuit supplied by transformer T2 asshown in Fig. 2. The firing voltage for the grids of the principal tubesI and 2 is also amplified through the tube 3 which is of the proper typefor the purpose.

The transformer T4 imposes on the grids G3 and G-4 of the amplifier tube3 sinusoidal voltages phased 180 apart, which also are respectively 120out of phase with the respective voltages applied to the anodes of thetubes I and 2, because transformer T-4 receives its primary supply fromthe secondary of transformer T2.

It will be noted that transformer TZ which supplies T4 is connectedacross wires LI and L-2 of the A. C. line, and transformer TI, whichaffects tubes I and 2, receives its supply from lines L-I and L3. Aswill be shown, the sinusoidal voltages on 3 are voltage rider waves on aD. C. control voltage applied from circuits IV, V, VI and VII to pointI8 of T4. Thus the major portions of the waves applied to grids G-I andG-Z will be fairly fiat, as will appear. Since the anodes and cathodesof tube 3 are connected across the reference voltage of the circuit II,a D. C. current similar in shape to a halfwave rectified current isdrawn from the system II, the waves being controlled alternately by thegrids G3 and G4. Since the actions of the grids G3 and G-4 alternatelymake each half of the tube 3 a half-wave rectifier, it will be seen thateach anode of the tube passes current alternately in accordance with theA. C. potential developed by the transformer T4. Hence the form of thedirect current furnished by the circuit II through each anode of tube 3is that of a current shaped in accordance with the wave of transformerT4. Thus a firing action occurs alternately on the anodes of tube 3 andthis firing will affect the grids GI and G--2 alternately andindependently.

Since the principal tubes I and 2 can each be fired only when itsappropriate anode voltage is positive, the firing must be and is doneduring that time for each tube (see Fig. 6). The anode sine waves IOI,I02 applied to tubes I and 2 are shown, the one for tube I as a solidline, and the one for tube 2 as a dash line. The firing voltage of tubeI is represented by dotted lines I03, and it will be noticed that thesedotted lines I 03 reappear in succeeding cycles under IOI. Dotted linesI04 represent the corresponding firing voltage line in the succeedingcycles belonging to tube 2. Therefore the dotted lines show the gridvoltages which would be necessary to fire the tubes I and 2. Lines I03and I04 for matched tubes are nearly the same but same variations Inshort, tubes I and 2 respectively tend are to be expected. The dot-dashline III represents the cusped but otherwise fairly flat D. C. voltagewave induced by the combination of the D. C. reference voltage on pointII of transformer T4, and the A. C. voltage applied to grid G-3 of tube3 by this same transformer T4. Double-dot-dash line III is thecorresponding line for grid G4. The D. C. lines I and I0! each comes toa peak once under each positive loop of lines "I and I02 respectively.

It will also be noticed that waves I06, I01 are inverse to the wavesIOI, I02 applied to tubes I and 2, and represent a series of half-wavetype D. C. conditions. These waves I06 and I01 may be shifted up anddown by adjusting a resistance R-0a (to be described) to effect variousfiring intersections with lines I03 and I04. This shifts the basic D. C.line L, which represents the D. C. control voltage at I0 of T4. Fig. 7i1- lustrates the result of such a shift. Wherever (Fig. 6) the curvesI06, I01 intersect the gridfiring voltage curves I03 and I04, the tubesI and 2 will be fired (see the cross-hatched areas), and since the cuspsof the curves I00 and I0! are relatively steep and can be made evensteeper than illustrated on the drawing, it is possible to sweep thesecurves through the entire lateral ranges of the firing voltages I03 andI04 much more effectively and with more definite control of the firingpoint of the tubes. Fig. 7 illustrates the maximum upward adjustment ofL and full firing of tubes I and 2. By using the cusps of the waves I06,I01 to intersect the broad crests of the grid-firing voltage curves I03.I04 and by inverting in respect to the anode voltages IOI, I02 appliedto tubes I and 2, the action is such as to eliminate any effect of onefiring voltage peak on another.

It is to be understood that the lines I 00 and I0! diagrammaticallyindicate the conditions above mentioned and that there may be minorvariations in the particular wave forms which carry out the statedprinciples. The important principle is that wherever either curve I06 orI01 intersects grid-firing voltage curve I03 or I04, respectively, toeffect firing, the respective curve I00 or I0! is concave upward.

Hence all tendency for so-called wave overlap in tubes I and 2 (such asoccurred in older systems) is eliminated. A great saving is effected intube life and erratic action avoided such as was heretofore caused bydifferent grid-firing voltage curves of difierent tubes. In other words,the major portions of the curves of the firing voltages I06 and I0! areflat, with the cusps as desired. Thus it is not possible, as heretofore,for the applied A. C. firing voltage substantially to intersect theentire firing voltage at once which with improperly matched tubes wouldcause one to assume a substantial overload.

Tests made with this equipment indicate that the control of the tubes ismuch more accurate than by the use of a broad 90 firing control wavewith a curving and gentle top, as previously used. This is because thetwo tubes I and 2 in the singlephase circuit are fired substantiallyequally due to the steepness of the approach between pairs of curvessuch as I05, I03; I01, I04. Unlike the old scheme, differences in tubegrid-firing voltage curves such as I03 and I04 will result in verylittle unbalance of firing load carried by tubes I and 2.

The mid-tap I0 of the secondary of the transformer T4 is connected withcircuit VII at I0 and the mid-tap of transformer T! is connected withthe circuit IV at 20. Circuits IV and V operate in voltage aidingsequence with the voltage from point 20. The circuit IV is a manuallyadjustable reference voltage circuit and the circuit V i an auxiliaryreference voltage circuit under speed control of machine P.

Circuit IV has a supply transformer T-0 which is energized from wiresL-I and L--! of the A. C. circuit. Circuit V is energized from atransformer T-'I, the primary of which is energized from the A. C.generator GNI driven by a mechanical power take-off PT from the machineP. The generator GN-I produces voltage only when the processing machineP is ope ative. When the processing machine P is shut 01!, then onlycircuit IV of the pair IV and V is relied upon for controllingenergization of coil CL. The purpose of the control by circuit IV duringthe time that the processing machine P is-not running is to controltension in the material under static conditions. For adjusting thecontrol by means of the operator, the potentiometer R-lo with a slidinpoint 20a is used.

The function of the auxiliary governing circuit V is to supply a part ofthe total reference voltage required while the processing machine isoperating. It will be seen that, when the machine P stops, the generatorGNI stops, so that this circuit V then no longer supplies a portion ofthe voltage, and a lower reference voltage results. Thus the totalcontrolled reference voltage is made up of the addition of voltages ofcircuits IV and V when the machine P is operating at the desired speed.plus the voltage from point 29. A function of circuit V is to hold thetension substantially constant on the processing material when the speedof the processing machine P is varied to accommodate the requirements ofdifferent raw materials.

In detail, circuit IV consists in a rectifier tube 1 the anodes of whichare connected with said transformer T6 energized from line wires L-I andL-Z. The center tap of this transformer T8 connects with potentiometersR0 and R-la. Potentiometer R-l is f the fixed type and point 28 isplaced in such a sition on 3-0 with respect to point 21 that a desiredminimum voltage will be obtained when the circuit V is cut out of actionby stoppage of the processing machine P. The resistance R-0a includes amanually controlled tap 20a for manually controlling the voltage takenfrom the circuit IV. A switch SW-l having three components has anormally closed contact at 20 and two normally opened contacts at 290and 30a. When the two normally opened contacts 290 and 30a are closedand the normally closed contact 20 i opened, resistance R-0 is removedand resistance R-la is substituted. On the other hand, when the contactsat 20a and 30a are opened and the one at 20 is closed, then theresistance R-l is effective and the resistance R -la is cut out. Thecircuit IV from point 20 or 200 is completed through the resistance R-I,choke K! and through the cathode of the tube 1. A condenser C2 and coldcathode tube 8 serve to maintain constant voltage conditions in thiscircuit. The solid arrows (see Fig. 5) in circuit IV show the localcurrent path through it. Tube 1 is heated through connection XX withT.l.

In detail, circuit V originates at the anodes of tube 0, being completedthrough the secondary or transformer T'|, point 20, variable resistanceR-t, point 24, choke K-4 and the cathode of circuit VI. This isolatescircuit V. Tube 8 is heated from YY of T-3.

As stated, the voltages from circuits IV and V and from point 29 opposethe voltage generated by the circuits VI and VII or by one of them.These voltages from IV, V and 29 all are directed to point 22 and passfrom that point to the grids G3 and G--4 of tube 3 via resistance R-l0,point 2|. variable resistance R-ll (or switch element SW-2-a) mid-pointl8 of transformer Tl, resistances R-l4 to the grids G--3 and (3-4 oftube 3. In Figs. 2 and 5 the voltage effects from point 29 to 22 areshown by dashed arrows. Beyond point 22, to the right and to i8, the sumof the voltage effects from IV, V and 29 is indicated by dot-dasharrows.

In detail, circuit VI is constituted by a rectifier tub. 8, the anodesof which are connected to the secondary of a transformer T-8. Theprimary of the transformer T8 is supplied by a variable voltagegenerator GN-2 driven from the field member F2 of clutch EC2, forexample. Voltage from the mid-tap of the secondary of transformer T-8 issupplied to point 22 in opposition to the voltage from circuits IV andV. The circuit VI is closed through resistance R-lli, point 2| and thecathode of tube 9. The condenser C-4 is used for the usual filteringpurpose. Local circulation is shown by the wavy arrows (Fig. 5). Theheater element of the cathode of tube 9 is fed from connection YY of thesecondary of the cathode transformer T3. Thus the circuit VI. like thecircuit V does not depend for energization upon the A. C. line. but uponthe speed of an independent generator, namely GN-2.

In detail, the circuit-VII is constituted by a rectifier tube I theanodes of which are connected to the secondary of a transformer T-S. Themiddle tap of a secondary of this transformer T-9 is connected to point20, the circuit being completed through resistance R-I i point l9, tothe cathode of the tube In, the condenser C-- serving filteringpurposes. Local circulation is here also shown by wavy arrows. Thevoltage of circuit VII is in the same sequence with the voltage fromcircuit VI, and the sum of these two voltages is in opposition to thatfrom the sum of the sequence voltages from the circuits IV and V andpoint 29. Point IQ of the circuit VII is connected to the mid-tap l8 ofthe secondary of transformer T-l .through a normally closed element b ofa switch SW--2. This switch element is by-passed by a normally openedelement a of the same switch SW-2. Thus circuit VII may be isolated byopening the switch element b and closing the switch element a. Tube I0is heated from YY of 'I'-3.

The primary of the transformer T-9 is energized from the A. C. circuitthrough means adapted to provide a voltage from circuit VII which issubstantially a straight-line function of the torque delivered by the A.C. motor WM. This is accomplished by means of a current transformer T-l0having a primary in the line L3 and a secondary which feeds the primaryof the transformer T-9. Resistance R- -l5 is connected across thesecond- 10 ary of the transformer T-l0. This provides a load.

Voltage transformer T-l I has its primary connected across the lines Lland L2 of the A. C. circuit. Resistance R-I3 is connected across itssecondary and has a variable tap 33 connected to the secondary oftransformer T-l 0. Point 34 of transformer T-H is connected to thevariable tap 22 of a resistance R-l2. By a suitable adjustment of theresistances R-l2 and R--l3, the transformer T-Il can be caused to buckdown that component of current generated in the transformer T-l0 as iscaused by the magnetizing requirements of the motor WM. The transformerT-I| is so connected and 32 and 33 are so adjusted that the voltagegenerated by TH cancels the voltage generated by the transformer Ti0when the motor is idling. Thus the loadampere curve of the motor issubstantially a straight line and the effect is to correct for powerfactor. The circuit between transformers T-9, Tl0 and T-|l may bereferred to as a transformer circuit component in governing circuit VIIfor obtaining a straight-line relationship between the voltage on T-9and torque on the motor WM. Potentiometer R--l3 is the one that bucksout magnetizing current and Rl 2 changes the slope of the straight-linevoltage-current relationship.

Since the current drawn in lines L3 by the motor WM is practicallyproportional to the torque of the motor, and since the transformer T-Hbucks out the magnetizing current, control is unaffected by suchmagnetizing current and the voltage output of transformer T9 istherefore substantially proportional to motor torque.

The motors WM, PW and PM operate at constant speed, being of theinduction type. The armature EA2 of the clutch EC2 overruns field F2 andshaft OP2. Thus the maximum speed of the reel WP-l will always be lessthan the maximum speed of the motor WM. Therefore, regardless of thecontrolled speed, EA--2 tends to overdrive the output member F-2, andtherefore, produces a tension in the finished material The speed withwhich the shaft OP2 can run is governed by the rate at which thematerial PM is delivered from the machine P. The eddy-current clutch EC2will slip under torque which increases with the slip between F2 and EA2.Hence the speed of the material FM virtually controls the speed of thereel WP-l and the function of the eddy-current clutch EC2 is to applynearly constant tension to the material. This requires regulation of thetorque produced by the clutch EC2. This torque should increase in afairly direct proportion from a low value when the material starts atthe core WPC, to a higher value at the rim. In other words, the torqueapplied must with the building up of the material, increase as closelyas is practicable to maintain the desired substantially constant tensionin the material. If the torque were not increased the tension wouldbecome gradually less and less. The practicable limits referred to inthe case of the present invention are uses wherein the ratio between afinal winding diameter to an initial winding diameter is not overapproximately 5:1.

Circuits I, II and III, considered independently of any other circuitshave constants such that tubes I and 2 are fired and energize coil CL.This is because the bridge points It and lGa are normally more positivethan bridge point I, for example, by about 75 volts. In other words.grids G| and G.2 of tubes I and 2 are held 1 1 positive to fire thesetubes. This corresponds to a certain couplin in clutch EC2 and a cercorespeed of the reel EC2.

The reference voltage produced by the combination of the circuits IV andV tends also toward firing of tubes l and 2 and increase of clutchexcitation. This is because negative potential from these circuits isapplied to the grids G3 and 6-4 of the tube 3. This biases tube 3 towardshutofi, thus robbin grids G-l and G-2 of tubes I and 2 of negativeelectrons. The firing action from tubes l and 2 is proportional to theaction of circuit IV or IV plus V.

Circuits VI and VII are connected so that their individual potentialsadd together and the total of these in opposition to the potentials ofcircuits IV and V tends to stop firing of tubes I and 2, which accountsfor the governing action of these circuits VI and VII. In other words,the circuits VI and VII tend to make the grids (31-3 and G-4 of tube 3more positive, thus favoring firing of tube 3 which supplies the gridsG-l and G2 of the tubes l and 2 with proportionate suppressing negativepotential.

At the beginnin of the wind-up with the reel WP-l practically empty, thereel speed must be its maximum running speed corresponding to the speedof the processing machine. At the start, the reel WPl will accelerate toany speed necessary to keep the material in tension. This maximum speedis provided by action of circuit IV wherein R-S is adjusted to give thisresult. As the reel accumulates material at a constant linear velocityof material, the angular velocity oi. the reel will tend to become lessand the EC-2 clutch slip will increase. Increased clutch slip slows downthe generator GN-2 which reduces the plus values contributed by it tothe grids G--3 and (3-4 of tube 3. This reduces the firing of tube 3,thus increasing the output of tubes l and 2. This tightens the clutchcoupling and increases the applied moment so that proper tension tendsto be maintained in PM in view of the growing lever arm caused by thegrowing diameter of the reel. However, in view of the inherentslip-torque characteristics of the clutch, this may or may not be thedesired rate of change to maintain substantially enough constant tensionin the material. Any incipient changes in tension in FM affect themoment or torque applied by FM to the roll WU at any given diameter ofthe latter. For example, an incipient increase in tension will increasetorque, and an incipient decrease in the tension of PM will decreasetorque applied to the roll. These incipient torque changes are of coursetransmitted to the motor WM. For example, an increase of torque requiredof the motor WM, due to increased tension in FM, would cause morecurrent to be drawn by the motor, thus increasing the plus output ofcircuit VII into the grids G3 and 6-4. This increases firing of tube 3and places more negative on grids Gl and G2 and reduces firin of tubes 1and 2. The result is less energization of the clutch coil and moreclutch slip, which incipiently decreases torque applied to the reel andcorrects said incipient increase in tension of FM. If the tension in PMwere incipiently to decrease, the action would be the inverse to thatjust described.

Thus it will be seen that decrease in reel speed due to increasing sizeof roll WU automatically calls into play reduced action from circuit VItending gradually to tighten the coupling and increase torque deliveredfrom the motor according to the growing moment arm of roll WU; but

- incipient changes in reactive torque due to incipient changes in thetension in FM are corrected through the action of circuit VII, theaction of this circuit VII being independent of sliptorquecharacteristics of the clutch and therefore corrective of anyundesirable deviation of this characteristic from what is desired.

It should also be noted that as the roll WU builds up, circuit VI, dueto reduction in speed of GN-Z, supplies less of the control voltage.circuit VII supplying more.

Thus circuits IV and V and circuit VI constitute the main balancingcontrol circuits as winding starts. As winding continues, circuit VIIprovides more of the governing control voltage and circuit VI furnishesless of the voltage Basically, circuit VI is responsible for what may becalled the proper increase in torque applying to the reel as the radiusarm increases (for substantially enough constant applied tangentialforce to FM) and circuit VII responds to torque changes resulting fromincipient variations in tension of FM and corrects for theseindependently of any undesirable slip-torque characteristics of theclutch.

Stated from another viewpoint, circuit VI provides a lower and lowerproportion of the voltage to control the firing of tubes l and 2 andcircuit VII supplies more and more of it as the action proceeds. Thusonce the process starts, circuit VI, which originally determined the topspeed for the empty core, slowly surrenders its control to circuit VII.

The running speed and threading speed can be set by the twopotentiometers (3-8 and R-Ba) in circuit IV; R-I controlling the runningspeed and R8a the threading speed. Operation of SW--3 transfers theconnections from the threading speed to the runnin speed by cutting outR-Ba and cutting in 11-. Switch SW-l is used to eliminate circuit V.Under certain conditions the control from the processing machine is notrequired and manual speed control by means of potentiometer R-O isrequired independently of the speed of the material. For this purposeswitch SW-| may be operated to cut out circuit V. Also, the torquecontrol circuit VII can be disconnected by means of switch SW-2. As anexample, it may be desirable to start the drive at a low threadingspeed. In this case resistance Rr-sa is temporarily cut in and theprocessing machine operated at a low speed. The material is thenthreaded through P and applied to the core of the wind-up reel WPI andafter a few revolutions at low speed, resistance R8a is cut out andresistance R' is cut in. The processing machine is then brought up torunning speed. at which speed the tension control functions, circuits Vand VII being connected.

From the above it is now clear that the circuits VI and VII cooperatewith each other, one of them (circuit VI) being responsive to speed andincreasing torque as the reel slows down, and the other (circuit VII)being sensitive to current demand of the motor and tendin to control thetorque according to the torque demands.

As to the pay-off reel UW-l, the system for operating it issubstantially the same as the one for the reel WPI. The only differenceis that the motor PW is driven in opposite sense to the motion of shaftOP-l so that the necessary tension or drag may be applied to the rawmaterial RM unwinding from the reel UW-l. The second circuit in unitCB-4 maintains the necessary constantly decreasing pay-off torque withincreased reverse slip. In this case the circuit VI (fed by acceleratinggenerator GN--3) gradually provides an increasing proportion of thevoltage which circuit VII initially provided. This is because generatorGN3 speeds up with decrease in diameter of roll W0. The current at firstdrawn by motor PW is high so that at first circuit VII in its controlactivities supplies the chief control voltage which is graduallyincreasingly supplied by circuit VI as the generator GN-J speeds up.Thus applied torque decreases as the pay-off roll becomes smaller andspeeds up. When considering the action of the pay-off control unit CB-lwhich is the same as the wind-up control unit CB-l, it should be notedthat what is indexed as generator GN--2 in Figs. 2 and becomes generatorGN-3; and what is indexed as clutch EC-2 in these figu-res becomesclutch EC-l. Also, what is motor WM becomes motor PW.

In Fig. 8 are shown exemplary ideal relationships between speed, torqueand control voltages.

Scale values have been selected for speed, torque,

amperes and volts such that the same numberson the various scalesrepresent magnitudes of more than one function.

GV is a straight-line curve of volts of circuit VI fed by generator GN-2or GN3, as the case may be. It will be recalled that these generatorswhich are controlled by reel speeds, serve the respective control unitsCB-l and CB-4 with voltages proportional to the respective reel speeds.The voltage output of circuit VI plotted against speed of WP-I is thusrepresented by line GV.

MA is a straight-line voltage curve of voltage output of circuit VII. Itwill be recalled that this straight-line function is due to thesubstantially straight-line function between the motor amperes drawn bymotor WM proportional to its torque. Thus curve MA represents volts ofVII plotted against torque required of EC-2 for constant tension.

The horizontal line B represents a selected base or core torque requiredfor the tension desired.

The straight-line curves Z-l, Z-Z, Z-3, Z--4 and Z--5 are torque-speedcurves which in common practice correctly enough represent theconditions required for different thicknesses of materials. Their slopesor declines increase with increasing thicknesses of materials. Toanother scale they also represent voltage changes required, duringreeling, of the transformer T-l0.-

For example, curve Z-l shows a speed for reel WP-l of 1000 R. P. M. whenthe roll WU is starting at the core WP-C. This corresponds to the lowertorque of 5. It also shows a speed of 500 R. P. M. of this reel when theroll WU has doubled its diameter, which corresponds to the higher torqueof 10. Since the voltage-speed curve GV is a straight line, a gradualchange of 1000 to 500 in speed means a gradual drop of to 5 in voltssupplied by the generator GN-2. This means a gradual drop of 5 voltsfrom circuit VI. This is accompanied by a gradual rise of 5 volts incircuit VII, or a ratio of 1:1 voltage exchange between VI and VII.Consider another example in line Z4 of the chart as follows: A drop of200 R. P. M. corresponds to a drop of 2 volts in circuit VI (caused by adrop in speed from 400 R. P. M. to 200 R. P. M. of the generator GN--2).

loss to gain being always 1:1. Also, the applied torque risesproportionally to the speed drop.

Potentiometer R-|2 sets the value of the torque at a given startingpoint or base, repre-v sented by line B. Potentiometer R-i2 having beenset, in order to adjust the system to the 2 volts interchange abovereferred to in the second example, it is merely necessary to adjust thevoltage output change of circuit VII to balance the voltage outputchange in circuit VI. This is done by adjusting point 19A ofpotentiometer R-l i. A trial of this can be made by using voltmetersacross the active portions of the resistances R-IO and R-l l Thus theuser may select any base torque for the starting condition on core WP-C(represented by line B) and by adjusting potentiometer R-ll there can bebrought about a rate of rise in voltage in circuit VII (due to torquechanges) equal to the rate of fall in voltage in circuit VI (due tospeed drop). All the while circuit VII exercises its governing controlof incipient deviations of torque from values which will maintain aconstant tension.

It must be remembered in addition that a basic top speed must bedetermined by adjusting, the potentiometer R-fl for the high speed pointwith a bare core WP-C at the start of operations.

As another specific example, suppose operation is desired underconditions of material for which curve Z5 is desired (Fig. 8). Thiscorresponds to the following conditions:

( 1) Top speed of reel at the start=200 R. P. M.

(2) Finish speed of reel at the end=l00 R. P. M.

( 3) Starting torque at the core WPC=5 units.

v(4) Finish torque at double the radius of the core=l0 units.

To obtain these conditions, potentiometer R8 is set for a voltage outputof circuit IV corresponding to a speed of 200 R. P. M. Thisautomatically takes into account the voltage from generator GN-Iactuated by the machine P. In other words, the speed of machine P is afactor in setting the speed of the reel. Potentiometer Ril is set sothat an interchange of 1 volt will occur as between circuits VI and VII,potentiometer Rr-|2 being set at a point equivalent to the proper numberof units of motor current, which is to say the proper number of units oftorque for the tension desired. This would be 5 units in the presentexample.

All circuits are energized when the machine starts. The clutch EC--2accelerates the drive up to the speed required of the reel WP-lnecessary to maintain a tension on the material which is then andthereafter controlled by circuit VII. As the speed drops the circuit VIIalso takes over the voltage supply relinquished by circuit VI as itfunctions to its control speed.

Commercial designations for the various tubes that are useful in thevarious locations are as follows: I

Tubes 4 and 6 VR-75 Values of other items in the circuit are designatedon the drawings.

It is to be understood that the described control may be used inconnection with the one reel only, since it is not always necessary tocontrol both reels.

Reference is hereby made under the requirements of Rule 43 to mycopending divisional applications of the present application as follows:Serial No. 655,699, filed March 20, 1946, for Control apparatus; andSerial No. 665,884, filed April 29, 1946 for Electronic controlapparatus, eventuated as Patent 2,458,454.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As many changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

I claim:

1. Material reeling apparatus comprising a rotary reel for a winding ofthe material, means for maintaining a substantially constant linearvelocity of the material, the winding having an increasing windingdiameter as the reel rotates whereby the speed of the reel decreases, anA. C. overrunning motor for turning the reel, an electric slip couplingbetween the motor and the reel, an electric field in said slip coupling,said decreasing reel speed increasing slip in the coupling accompaniedby an increase in driving torque applied by the motor through thecoupling and accompanied by an increase in the motor current, andcircuit control means responsive to said increase in motor current andresponsive to incipient reduction in reel speed adapted to control theenergization of said field so as to adjust the slip in said coupling soas to produce a torque delivered from the motor to the reel which willmaintain substantially constant tension in said material as the windingdiameter increases.

2. Tension control apparatus comprising a reel, an A. C. motor, an A. C.circuit therefor, an eddycurrent slip clutch connecting the motor withthe reel, a field winding in the clutch, a principal rectifier circuitfeeding said clutch winding, a gridcontrolled rectifier tube in saidcircuit, a grid-controlled control tube controlling the grid of therectifier tube, a main reference voltage circuit connected with saidcontrol tube and said principal rectifier circuit so that normally saidrectifier tube fires into said winding to energize it, a grid for thecontrol tube, a governing rectifier circuit controlling said grid, acurrent transformer in one leg of said A. C. circuit, said transformerfeeding said last-named governing rectifier circuit, whereby increasedcurrent delivered to said motor under increased load conditions thereonbiases said control tube toward firing so as to bias the grid in therectifier tube toward a condition of lower output from the rectifiertube.

3. Tension control apparatus comprising a reel, an A. C. motor, aneddy-current slip clutch connecting the motor with the reel, 8. fieldwinding in the clutch, an A. C. circuit serving the motor, a principalrectifier circuit feeding said clutch winding, a grid-controlledrectifier tube in said circuit, a grid-controlled control tubecontrolling the grid of the rectifier tube, a main reference voltagecircuit connected with said control tube and said principal rectifiercircuit so that normally said rectifier tube fires into said winding, agrid for the control tube, a governing rectifier circuit controllingsaid grid, 9. current transformer in one leg of said A. C. circuit, saidtransformer feeding said last-named governing rectifier circuit, wherebyincreased current delivered to said motor under increased loadconditions thereon biases said control tube toward firing so as to biasthe grid in the rectifier tube toward a condition of lower output fromthe rectifier tube, a speed-control rectifier circuit, a generatordriven by the clutch and feeding the speed-control circuit, saidspeed-control circuit in response to decreased generator speed andoutput biasing said control tube toward reduced output, whereby saidgridcontrolled rectifier tube in the main rectifier circuit tends toproduce higher output into said clutch field winding, except as modifiedby action from said current-controlled governing circuit.

4. Material reeling apparatus comprising a rotary reel for a winding ofthe material, said winding being ofchanging diameter, an A. C. motor forcontrolling rotation of the reel and supplied by an A. C. circuit, anelectric slip coupling between said motor and the reel, a D. C. fieldwinding in the slip coupling, a D. C. rectifier circuit feeding saidfield winding and including a gridcontrolled rectifier tube, a currenttransformer having a secondary and a primary, the latter being connectedin one leg of said A. C. circuit to the motor, a control circuitconnected to the secondary of said current transformer and suppliedthereby and controlling said rectifier circuit through the grid of saidtube, and a voltage transformer having a primary connected to the A. C.circuit and connected with the current transformer by means adapted toproduce a controlling action by said control circuit which issubstantially proportional to the torque on said motor.

5. Material reeling apparatus comprising means for moving a length ofthe material at substantially constant speed, a rotary rcel for awinding of the material which winding is of changing diameter, an A. C.motor for driving the reel and supplied by an A. C. circuit, an electricslip coupling between said motor and the reel, a D. C. field winding inthe slip coupling, a D. C. rectifier circuit feeding said field windingand including a grid-controlled rectifier tube, a current transformerhaving a primary connected in one leg of said A. C. circuit to the motorand having a secondary, a control circuit supplied by said secondary andcontrolling said rectifier circuit through the grid of said tube,whereby the energization of said field winding is caused to respond tochange in current drawn by the motor, and means connected to the controlcircuit whereby the torque supplied by the slip coupling to the reelfrom the motor is caused substantially constantly to produce torquethrough the reel which will apply a substantially constant tension tosaid length of material.

6. Material reeling apparatus comprising means for moving a length ofmaterial at predetermined velocity, a rotary reel for supporting awinding of the material which winding changes in diameter, an A. C.motor for controlling rotation of the reel and being supplied by an A.C. circuit, an eddy-current slip coupling between the motor and thereel, a D. C. field winding in the slip coupling, a D. C. rectifiercircuit feeding said field winding and including a grid-controlledrectifier tube, a main reference voltage circuit and coordinated bridgecircuit adapted normally to maintain a positive value of the tube gridto fire said rectifier circuit into said winding, a sec- 17 ndgrid-controlled rectifier tube forming one branch of said bridgecircuit, auxiliary D. C. reference voltage circuit means adapted toapply to the grid of the second tube negative voltage tending tosuppress said second tube and permit said firing of the first tube, agoverning circuit controlling the grid of said second tube and operatingin negative voltage opposition to said adjustable reference voltagecircuit and tending to make more positive the grid of said second tubeand tending to fire the second tube into the grid of the first tube toexert controlled suppression of its firing into said winding.

7. Material reeling apparatus comprising means for substantiallyconstantly moving a length of material, a rotary reel for supporting awinding of the material which winding is of changing diameter, an A. C.motor for controlling rotation of the reel and supplied by an A. C.circuit, an eddy-current slip coupling between the motor and the reel, aD. C. field winding in the slip coupling, a D. C. rectifier circuitfeeding said field winding and including a grid-controlled rectifiertube, a main reference voltage circuit and coordinated bridge circuitadapted normally to maintain a positive value of the tube grid to firesaid rectifier circuit into said winding, a second grid-controlledrectifier tube forming one branch of said bridge circuit, adjustable D.C. reference voltage circuit means adapted to apply to the grid of thesecond tube negative voltage tending to suppress said second tube andpermit continued firing of the first tube, a governing circuit having aD. C. section controlling the grid of said second tube and operating innegative voltage opposition to said adjustable reference voltage circuitand tending to fire the second tube into the grid of the first tube tobias said first tube toward suppression of its firing into saidwinding,a current transformer responsive to current in one leg of said A. C.circuit supplying the motor and having a secondary, and a transformersection in said governing circuit connected with said secondary andfeeding into said governing circuit.

8. Material reeling apparatus comprising means for substantiallyconstantly moving a length of material, a rotary reel for supporting awinding of the material which winding is of changing diameter, an A. C.motor for controlling rotation of the reel and supplied by an A. C.circuit, an eddy-current slip coupling between the motor and the reel, aD. C. field winding in the slip coupling, a D. C. rectifier circuitfeeding said field winding and including a grid-controlled rectifiertube, a main reference voltage circuit and coordinated bridge circuitadapted normally to maintain a positive value of the tube grid to firesaid rectifier circuit into said winding, a second grid-controlledrectifier and amplifier tube forming one branch of said bridge circuit,adjustable D. C. reference voltage circuit means adapted to apply to thegrid of the second tube negative voltage tending to suppress said secondtube and permit continued firing of the first tube, a governing D. C.circuit having a D. C. section controlling the grid of said second tubeand operating in negative voltage opposition to said adjustablereference voltage circuit and tending to fire the second tube into thegrid of the first tube to bias said first tube toward suppression of itsfiring into said winding, a current transformer responsive to current inone leg of said A. C. circuit supplying the motor and having asecondary, a transformer section in said governing circuit connectedwith said secondary and feeding into said governing circuit, and avoltage transformer connected to said A. C. circuit and cooperating withsaid transformer section to produce a D. C. potential in said governingvoltage circuit which is proportional to the torque required of saidmotor in order to maintain a substantially constant tension in saidmaterial.

9. Tensioning apparatus comprising a reel, an A. C. motor associatedwith the reel, an eddy-current slip clutch between the motor and thereel, a field winding in said clutch, an A. C. circuit feeding saidmotor, a principal rectifier circuit fed by said A. C. circuit andincluding grid-controlled rectifier tubes firing into said coil, acontrolled amplifier tube controlling said rectifier tubes, a mainreference voltage circuit, an adjustable reference voltage circuitassociated with said main reference voltage circuit, an auxiliaryreference voltage circuit connected with said ad- Justable referencevoltage circuit, said reference voltage circuits being connected withsaid amplifier tube in a manner tending to prevent the amplifier tubefrom firing into the grids of the rectifier tubes thus favoring firingof the latter into said coil, an A. C. generator driven by the clutch, agoverning rectifier circuit fed by the generator, a second governingrectifier circuit, a current transformer fed by one leg of the A. C.circuit which feeds the motor and supplying said second governingcircuit, said governing circuits being connected in voltage oppositionwith respect to said adjustable and auxiliary reference voltage circuitsand controlling firing of the amplifier tube into the grids of thefirst-named rectifier tubes to exert controlling cut-off action on saidtubes.

'10. A tension control apparatus comprising a reel for material beingwound, an A. C. motor for driving the reel, an A. C. circuit for themotor,

an'eddyj-current slip clutch connecting the motor with the reel, a fieldwinding in said clutch, a first A. C. generator driven by the reel, 9.second A. C. generator driven in accordance with linear speed of thematerial approaching the reel, a rectifier circuit fed from said A. C.circuit and including a rectifier tube firing into said clutch coil, agrid controlling said tube, a control tube for said grid, a grid controlfor said control tube,

a basic reference voltage circuit connected with the grid of saidrectifier tube normally causing said tube to fire into said coil, anadditional reference voltage circuit associated with said main referencevoltage circuit and fed by said second generator, a-governor circuit fedby said first generator, said governing circuit affecting the grid ofthe control tube decreasingly to cause said control tube to fire intothe grid of the rectifier tube as reel speed decreases to reduce firingof the latter, and a circuit fed by means responsive to current in theA. C. circuit to the motor, said last-named circuit upon increase incurrent increasingly firing the control tube into the grid of saidrectifier tube whereby the latter tends to be cut off and slip isincreased in said clutch to control tension in said'material.

11. A tension control apparatus comprising a reel for material beingwound, an A. C. motor for driving the reel, an A. C. circuit for themotor, an eddy-current slip clutch connecting the motor with the reel, afield winding in said clutch, an A. C. generator driven with the reel,an A. C. generator driven in accordance with linear speed of thematerial approaching the reel, a rectifier circuit fed from said A. C.circuit and including rectifier tubes firing into said field winding ofthe clutch, grids controlling said tubes, a control tube having anodesrespectively feeding said grids, grid controls for the anodes of saidcontrol tube, a basic reference voltage circuit connected with the gridsof said rectifier tubes biasing said tubes to fire into said coil, anadditional reference voltage circuit associated with said main referencevoltage circuit and fed by said generator controlled by the linearvelocity of the material, a governor circuit fed by said generator whichis driven with the reel, said governor circuit controllin the grids ofthe control tube with decreased reel speed to cause the anodes of saidcontrol tube decreasingly to fire into the grids of the rectifier tubes,thereby controllably to increase firing of the latter, and a governingcircuit fed by means responsive to current in the A. C. circuit to themotor as the motor current increases with any increased load, saidlastnamed circuit controlling the grids of the control tube so as toincrease firing in response to increased current in the A. C. circuit,firing being into the grids of said rectifier tubes whereby therectifier tubes tend to fire less and whereby slip is increased in saidclutch.

12. Material reeling apparatus comprising a rotary reel for a winding ofmaterial to be formed on the reel under substantially constant tensionand speed of the material approaching the reel, the winding having achanging winding diameter as the reel rotates, a motor for turning thereel, an electric slip coupling between the motor and the reel, a fieldwinding in the slip coupling, means for energizing the windingresponsive to change of slip in the coupling as the winding diameterchanges and tightening or loosening the coupling in a substantiallydirect proportion to the winding diameter, and means responsive to loadchange on the motor caused by increased slip due to changing windingdiameter and any incipient variation in tension adapted to maintain saidtension substantially constant.

13. Material reeling apparatus comprising a rotary reel for a winding,the material to be applied to the reel under substantially constanttension and speed, the winding having a changing winding diameter as thereel rotates, a motor for turning the reel, an electric slip couplingbetween the motor and the reel, a field winding in the slip coupling,means for energizing the winding responsive to change of slip in thecoupling as the winding diameter changes and consequently tightening orloosening the coupling in a substantially direct proportion to thewinding diameter, means responsive to load change on the motor caused byincreased slip due to any changing winding diameter and also caused byincipient variation in tension for maintaining said tensionsubstantially constant, said last-named means including a currenttransformer responsive to all components of the current supplied to themotor except the motor magnetizing component of said current.

14. Tension control means for a length of material comprising a pay-oil.reel and a wind-up reel therefor, means for controlling the linearvelocity of said material between reels, both of said reels turning inthe same direction, a driving motor associated with the wind-up reel androtary in the same direction, a retarding motor associated with thepay-oil" reel and rotary in the opposite direction, electric slipclutches magnetically connecting the respective motors with therespective reels, field windings in said clutches, means for energizingsaid field windlugs to vary the intensities of the magnetic couplingsthrough the clutches in response to their respective slips, so that thetorques applied to the reels are respectively in a substantially directproportion to the respective winding radii, and means responsive tocurrent and voltage supplied respectively to said motors forrespectively controlling slip of said clutches to maintain constant thetension in said material.

15. Tension control apparatus comprising a reel, an A. C. motor, an A.C. circuit thereior, an eddy-current slip clutch connecting the motorwith the reel, a field winding in the clutch, a principal rectifiercircuit feeding said clutch winding, a grid-controlled rectifier tube insaid circuit, a grid-controlled control tube controlling the grid of therectifier tube, a main reference voltage circuit connected with saidcontrol tube and said principal rectifier circuit and biasing saidrectifier tube to fire into said winding to energize it, a grid for thecontrol tube, a governing rectifier circuit controlling said grid, acurrent transformer in one leg of said A. C, circuit, said transformerfeeding said last-named governing rectifier circuit, whereby increasedcurrent delivered to said motor under increased load conditions thereonbiases said control tube toward firing so as to bias the grid in therectifier tube toward a condition of lower output from the rectifiertube, and a governing circuit controlled by the speed of the reel andalso controlling the grid of the control tube so that the control tubedecreasingly or increasingly fires with decreasing and increasing speedsrespectively of the reel, whereby the rectifier tube respectivelyincreasingly or decreasingly energizes the clutch coil for controllingtorque applied to the reel in substantial accordance with the rolldiameter of any material being wound on the reel. 1

16. Material reeling apparatus comprising an electric slip coupling, areel for the material driven by said coupling, an electric field meansin the coupling determining its torque transmission, a generator drivenin accordance with reel speed, a reference voltage circuit controllingenergization of said field means and determining the speed of the reelat minimum diameter of material thereon, a speed-responsive voltagecircuit responsive to action of said generator and additionallycontrolling energization of said field coil to increase or decreasetorque transmitted through the coupling with speed decrease or increaserespectively, and a torque control circuit connected with said speedcontrol circuit and also controlling said field to maintainpredetermined torque transmitted through the coupling at a given speed,whereby substantially constant tension is maintained in the material atall speeds.

1'7. Material reeling apparatus comprising an electric slip coupling, areel for the material and driven by said coupling, an electric field inthe coupling determining its torque transmission, a generator driven inaccordance with reel speed, an adjustable reference voltage circuitcontrolling energization of said field means and determining the speedof the reel at minimum diameter of material thereon, a speed-responsivevoltage circuit responsive to action of said generator and additionallycontrolling energization of said field coil to increase or decreasetorque transmitted through the coupling with speed decrease or increaserespectively, a torque control circuit connected with said speed controlcircuit and also controlling said field to maintain predetermined torquetransmitted through the coupling at a given speed, and two adjustmentmeans in said torque control circuit, one of which determines the slopeof the torque-speed curve required for various thicknesses of materialsto be reeled, and the other of which determines equal but inversechanges in the voltages supplied by the speed control and torque controlcircuits respectively.

18. Tension control means for a length of material comprising a pay-citreel therefor, means for controlling the linear velocity of saidmaterial as it moves from the reel, a retarding motor associated withsaid pay-oif reel and rotary in the opposite direction, an electric slipclutch magnetically connecting the motor with the reel, a field windingin said clutch, means for energizing said fleld winding to vary theintensity or the magnetic coupling through the clutch in response to itsslip, so that the torque applied to the reel is in a substantiallydirect proportion to the unwinding radii, and means responsive tocurrent supply to the motor also for controlling slip of the clutch tomaintain substantially constant the tension in said material.

ANTHONY WINTHER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

